Microarrays technology, based on receptor-analyte interaction, is replacing the conventional assays using gels, filters and columns, with glass chips capable of storing tens of thousands of probes (nucleic acid sequences), proteins, etc, which provide information on the levels of gene expression, protein synthesis, single nucleotide polymorphisms or SNPs, etc.
The surfaces employed for microarrays must advantageously be flat and even, so as to make it possible to anchor of a large number (e.g. hundreds or thousands) of spatially arranged molecules (probes, proteins, etc.). The detection and quantification of results is carried out by means of fluorescence or colorimetry and, to a lesser extent, by mass spectroscopy, using molecules functionalized with a suitable marker for this purpose. The markers most often used are fluorophores with excitation wavelengths of around 450 nm and emissions within the 500 nm-800 nm range.
Due to its optical transparency, low autofluoresence, chemical properties, thermal stability and price, glass if the reference material employed as a support in this technology, By means of chemical modification, via silanization, specific functional groups can be added, such as amine-epoxy-carboxylic acid- or aldehyde groups (Cheung, V G, et al. Nature Genetics (suppl), 1999, 21, 15-19; Zammatteo, N. et al, J. Analyt. Biochem, 2000, 283, 143-150), which make the covalent anchoring of oligonucleotides or single-stranded DNA (ssDNA) molecules possible for the subsequent analysis thereof.
However, the great interest in the study of new supports and the large market existing in this field of work has led to the search for new alternative materials. Of all these materials, synthetic polymer materials display highly attractive chemical and mechanical properties, a good price, a high degree of flexibility and biocompatibility and good optical and mechanical properties, as well as being easy to manufacture. In addition thereto, they can be used as interactive supports, given that they increase the working capacity on affording the possibility of incorporating the treatment of the sample and the detection of the results. Similarly, detection techniques other than fluorescence can be used, thus making the assays faster and simpler. For all of the abovementioned reasons, polymer materials have become an alternative to glass for the manufacture of microarrays.
Apart from the above, the development of microelectromechanical systems for bioassays (BioMEMS) focuses many of the applications thereof on Genomics and Proteomics. This type of devices integrates chemical assays with the preparation of the sample and the detection thereof (results readout). For the manufacture thereof, synthetic polymer materials (e.g. polycarbonates, polymethacrylates, polystyrenes, polyamides, polysiloxanes, etc) or natural materials (silicon, silicon oxide, etc.), these latter materials coming from the electronics industry, are generally used.
Audio-video compact discs (CDs) are a promising platform for building this type of devices (EP 1189062; Kido, H. et al., Analytica Chimica Acta, 2000, 411, 1-11). A standard CD is comprised of a polycarbonate base on which the information is recorded, coated with a metal layer of aluminum, nickel, gold or silver, or rather with a layer of light-sensitive dye, protected by a polymethacrylate coating. One of the most outstanding advantages of CDs as supports for microarrays is the large surface area available, low background fluorescence, the use of materials of high optical and mechanical quality in their manufacture, their low price and their easy handling. Similarly, these supports afford the possibility of quadrangular, circular or spiral spatial organization of the probes and proteins printed, providing numerical information for identifying each spot, it being possible to use one of the sides of the CD for conducting the biochemical assays and the detection thereof, and the other side for saving the information, the results being read in all cases by means of modified CD-readers (U.S. Pat. No. 6,395,562 and WO2003/087827). The aforesaid could be applied to DVDs, given that they are of the same composition as CDs.
Chemically modifying polymer surfaces for the purpose of fine-tuning supports for chemical assays has still as yet not been developed to any great degree. This field of work has been approached by using different strategies, the techniques most employed being based on the plasma, flame, electrical discharge, surface grafting, chemical reaction and vapor deposition treatment (Chan. C M., Polymer Surface Modification and Characterization, 1993, Munich:Hansen).
Studies have been published describing surface modifications of different types of polymers (US2002/0197467). A study has been made of the surface modification of methyl polymethacrylate by means of aminolysis of the methyl ester with lithium amide in aliphatic diamines and the application thereof in devices for microfluids (Soper, S. A. et al., Analytica Chimica Acta, 2002, 470, 87-99; Anal. Chem., 2003, 75, 2975-84). There are also other examples of surface modification of methyl polymethacrylate based on the reduction of the ester groups followed by a treatment with different organosilanes (Cheng J-Y., et al, Sensors & Actuators B99, 2004, 186-96). One drawback of these methods lies in the need of working with organic solvents which modify the properties of the plastic.
Surface modification methods for polycarbonate have also been described. Most of these methods use the oxidation/sulphonation of the rings or rather the hydrolysis of the carbonate (e.g. WO99/35499, EP0487854). These methods are, however, not very effective.
Despite the different surface modifying methods described in the state of the art, a great need still as yet exists of designing alternative methods for the chemical modification of polymers which will make it possible to provide surfaces of the desired properties whist ensuring that the optical and mechanical properties of the original polymer will remain unchanged.